Ponderings

Something from nothing?

Every now and again I plan to post something that is not main stream physics, and this is one of them. For those interested in "proper" physics, you may want to give this one a miss. This is all just pure speculation on my part.

This post is my musings on the conservation of energy. 

Before we get started, I have posted previously  on the idea that I think that the angular and linear momentum of the universe is actually zero. I have no proof of this and there is currently no accepted answer to the question. In fact it is actually very difficult to even ask the question, because we end up having to make a lot of assumptions or guesses. Firstly, we don't know that the big bang theory is correct. Yet this will definitely have an impact on any answer we try to derive. 

Conservation of energy works on all the tests we have done on a small scale, so I am going to assume that the universe is a good sport and is happy to play by the rules. So, total conservation of momentum, angular and linear, is zero. I go further to suggest that the total electric charge of the universe is also zero.

Finally to the subject of this post. I think that the total energy of the entire universe is zero. Or, if not zero, some fixed value.  This is a bit of a wild idea, no doubt about it. We have back ground radiation, we have planets and suns all with mass, which according to Einstein is just energy sort of condensed. If you add up all the electro magnetic radiation in the universe and add up all the mass of all the planets and stars you most certainly do not get zero. So, just what am I going on about. Well ..

The net energy in the universe is zero or a constant value. All the energy we see is offset by a SpaceTime energy field. I don't think that it makes sense for SpaceTime to just be some frame of reference.

Time is real. I may not understand time, I know that there is a past I can remember it. I know that there is a future and I will die at some point in that future. This is an absolute fact. While I may not know the hour of the event, I am 100% certain that it will come to pass. Therefore the future which contains set results exists.  There is more on this idea in another post. But for today I will content myself with the idea that SpaceTime is not an abstract idea but something that is an integral part of the real universe.

So say SpaceTime is actually the equivalent of negative energy and negative mass.  We believe that the universe it about 13 billion years old and continues to get older a day at a time. So if this means that we're making more SpaceTime each and every second of each and every day and if this is the case then this must be balanced by real matter and energy. I think that this is the case.

If this was so, we would expect to see the conservation of energy/mass violated at some point as the new mass and energy suddenly pops into existence. This has not been seen yet. So it is either wrong, or we have not seen the conditions under which this may actually happen.

I think that the conditions for energy/matter to "spontaneously" occur are low vacuum and low gravitational field. The only places we see this are deep space. Further, I have a feeling that the particles that appear as if by magic are probably neutrons. Which decay pretty sharpishly into protons, electrons and an anti electron neutrinos.

Can I prove any of this? not at the moment no, but I am working on it.

Black Holes - Part 2

The Great Escape

This is the second post on the subject of Black Holes. In the first post I went on a little about General Relativity and how it describes the universe. The post then went on to discuss the idea of escape velocity and how it could be possible to have an escape velocity that was actually greater than the speed of light. In other words nothing, including light would be able to escape from such an object.

The secrets to most of this are held in the Einstein Field Equations, which as mentioned are rather difficult to understand. But that has not stopped some of the braver souls out there.

In 1915, Karl Schwarzschild managed to get a solution to the Einstein Field Equations for the gravitational field outside a non-rotating sphere. The solution had a rather bizarre property in that it contained a radius which became known as the Schwarzschild radius. It seemed that if all the mass of the an object was compressed within this sphere then it would be possible to create a situation where the escape velocity was greater than the speed of light.

Further, the gravity resulting from having so much mass compressed into this sphere would be the creation of a singularity.  The physical significance of this singularity was debated on and off during the decades taht followed.

In 1931 Subrahmanyan Chandrasekhar showed that if a star was above a certain mass then it could actually collapse under its own gravity (when its fuel ran out) and shrink to a size smaller than the Schwarzschild radius thus become what has been described as a singularity. The star would shrink and get so small that the entire star would end up smaller than an atom while having pretty much the same mass. The singularity is so small that is has no physical size!

(I'll be straight with you, I have a serious problem with the idea of a singularity because it is so small that it doesn't actually exist! and yet we are told that it does exist! Personally I can't help thinking that when this catastrophic collapse happens we get ourselves a type of Bose Einstein condensate, more on this in another post.)

For now we will continue with conventional wisdom. The big star collapses to give a singularity with a massive gravity. As the distance from the singularity increases the gravity will start to shrink and so will the escape velocity. At some distance from the singularity the gravity would have diminished enough that the escape velocity is the speed of light. Any further and light can happily escape the clutches of the singularity. This distance when the escape velocity equals the speed of light is known as the event horizon which is the Schwarzschild radius.

It is interesting to note that general acceptance of the possibility of a black hole did not occur until the second half of the 20th century. It was only around about  the1950s, just prior to the death of Einstein, that General Relativity entered mainstream theoretical physics. The next 30 years can be described as a golden age of General Relativity and Black hole theories.

This was helped by the discovery of pulsars by a hero of mine,  Jocelyn Bell Burnel, this will be covered in a later post, which were shown to be neutron stars. If neutron stars could exist why not black holes?


During the 60s and 70s contributions from Roger Penrose and Stephen Hawking, James Bardeen and Jacob Bekenstein helped solidify the ideas of black holes by developing a number of theories describing the properties and behavior. It was during this time the term Black hole was first introduced to describe a singularity and is usually attributed to John Wheeler.


But  here is the thing. Although all these really clever guys have spent years pondering and coming up with theories and ideas, the question remains do they actually exist?

Well the answer is we still don’t know. What we do know is that Einstein’s theory of general relativity made a number of other predictions that are backed up by experiment. So if we work on the bases that if these positive results show that the theory may be correct then it makes sense to assume that some other predictions, such as black holes, may also be true. That is why we THINK there are black holes, but we don’t know for sure.

Another theory may come along which explains the things that Einstein got right and have been tested and then goes on to show why black holes can't exist!

Personally I don't think black holes do exist. It just doesn't seem right to me. I accept neutron stars and I can believe that gravity can get so great that even the Pauli exclusion principle (the theory explaining why neutron stars don't collapse to black holes) may be over come, but that is where it ends for me. See I think at this point the following may happen.

The star collapses so that it is smaller than the event horizon. Neutrons (fermions) pair up and become bosons, the star then collapses into a Bose Einstein condensate.  Rather than continuing the collapse into a singularity, quantum effects take over and become apparent on a macroscopic scale. We then get something akin to Quantum tunneling where a particle tunnels through a barrier that it classically could not surmount. In this case the particles actually tunnel through the event horizon. Due to the increased gravity, particles get squeezed out much like toothpaste and appear, due to the rapid rotation of the "black hole" as a disk.

You can cross the event horizon and escape again. 

In this solution we get an event horizon, but what we don't get is a singularity.

So I suppose I do think there may be black holes, but I don't believe that there are singularities at the center.

Silicon and the Czochralski process

Most people have no idea what the Czochralski process actually is and yet it is the first step in a chain of events and processes that have changed the world. The reason you can read this now is because of the Czochralski. This post is about his fantastic process.

The Czochralski process is a method of crystal growth that is named after Jan Czochralski who discovered the method in 1916 while investigating the crystallization rate of metals. This process is now used to produce single crystals of semiconductors such as silicon, germanium and gallium arsenide. It can also be used to create crystals of palladium, platinum, silver, gold and synthetic gemstones.

The most important use of this process is the growth of large cylindrical single crystals of silicon. It is these that are turned into the silicon chips used in computers, phones, DVD payers and many other devices.

The process:

Silicon is the most abundant solid element on earth, being second only to oxygen and it makes up more than 25% of the earth’s crust. It is almost always found in compounds rather than pure silicon. For silicon chips we need pure silicon. It is not possible to get the high quality, high purity silicon required for computer chips in a single step. In fact it takes a number of steps. The Czochralski process is the final step which results in high purity silicon.

Silicon typically starts out as an iron-silicon alloy and accounts for about 80% of the worlds production of  elemental silicon. 1- 2% of this is purified to be used in the electronics industry.

The use of silicon in semiconductor devices requires very pure silicon (>99.9%). This can be extracted directly from solid silica or other silicon compounds by molten salt electrolysis a process known since the 1850s.

The next step is to produce a higher purity silicon for use in the crucible. The silicon is purified further using a chemical process known as the Siemens process. The Siemens process itself starts with a high purity seed rod, silicon is then deposited onto this via a chemical reaction. The rod basically gets fatter and fatter and is very pure.

The rod from the Siemens process can then be broken up and placed in the Crucible ready for the next stage.

The silicon is melted in a crucible (typically quartz, which is silicon!) and a small Czochralski silicon crystal is lowered into the melt. At this point impurities such as boron of phosphorus can be introduced to alter the final silicon. This is done in a very controlled way using very specific amounts. So instead of pure silicon we get "doped" silicon known as either n-type or p-type silicon. Or the impurities can be left out an a pure silicon crystal is grown.

The temperature of the silicon in the crucible is very tightly controlled and is just above the melting temperature of silicon. The seed crystal is attached to a rod that is rotated and pulled upwards at the same time. The speed of rotation and the speed the crystal is pulled upwards determines the width of the final crystal. This is typically done in an argon atmosphere.

The finished crystals can be very large, crystals with a 400 mm diameter (that is a circumference of over a meter!) and 1 to 2 meters in length are standard these days. These large crystals are then cut up into wafers thick enough to be handled during the chip making process. This thickness is usually about 3/4 of a mm thick, so a 1 meter crystal will give about 1200 wafers.

The crystal is cut up using a special wire saw that can cut hundreds of slices simultaneously. This can take several hours. The shape edges are then smoothed down to prevent damage later in the process.  Then the wafers are mounted and polished using a slurry, this is a liquid with very small particles in it that act as an abrasive. The result is very flat wafers.

The wafers are then etched with nitric, hydrofluoric and acetic acids producing an even smoother and cleaner surface. This is then ready for chip production.

The silicon wafers used at the beginning of the integrated circuit making process must first be refined to "nine nines" purity (99.9999999%), a process which as we have seen requires repeated applications of refining technology.

That is pretty much it. Though by all accounts much of this is still an art form as much as it is process. There are some real artists out there it seems. 

Non-inertial Frame Of Reference

Coriolis forces in a hurricane

I recently did a post on Inertial Frames of Reference (IFoR) so I thought I best complete the picture by doing a post on Non-inertial frames of reference. As we saw in the other post the IFoR turned out to be very similar to my garage. The Non IFoR or NIFoR for short is not like my garage.

Technically a  non-inertial reference frame is a frame of reference that is undergoing acceleration with respect to an inertial frame, a bit like a car decelerating when it is pulling into say, a garage.

So a garage is an inertial reference frame and a car accelerating out of a garage or slowing as it enters the garage is a non-inertial reference frame. Yes, but this doesn't really help, because you would have to be a lunatic to be performing scientific experiments in a car while driving. That said, it is a non-inertial reference frame.

The odd thing is that things get really complicated when you introduce accelerations. The laws of motion in non-inertial frames get more complex and vary from frame to frame depending on the acceleration. Not only that but you have to start inventing forces to account for the observed motion. These include the centrifugal force and the Coriolis force.

Now many people have heard of the centrifugal force, it is the thing that tries to throw you out of the ride at the fair. You feel it, it must exist. Firstly, the centrifugal force is generally confused with the centripetal force. The centripetal force, in the case of something like the earth rotating round the sun, being the force towards the centre of the earth.

The centrifugal force is sometimes called an inertial force or a fictitious force, but this is a "technical" term and all it means is that it disappears when you are stationary, for example, you are in a car going in a straight line at a constant speed, no centrifugal force, you go round a corner all of a sudden we are feeling a force. 

Coriolis Force

Another force is the Coriolis force or Coriolis effect, named after Gaspard Gustave Coriolis who lived in the first half of the 19th century. One cause, or example of the Coriolis effect is that caused by the rotation of the earth and the inertia of the a mass experiencing this rotation. The force is proportional to the mass and the rotation rate. Larger the mass and the speed of rotation the larger the force.

Imagine a disk just like the one here, which does NOT rotate. We roll a marble from the center to the edge, it moves in a straight line.

We do it again, only this time we let the disk rotate at a constant speed. Now if I am standing on the disk in the middle I don't notice this force because I am rotating at a constant velocity, but all of a sudden I notice that the marble is not traveling in a  straight line, but is now moving along a bended path. Right away I think there must be a force acting to cause this effect.  This fictitious "force" is the Coriolis force F_c

 The idea of the Coriolis and Centrifugal forces is that they are correction factors that do not exist in a non-accelerating "inertial" system, so we say that they are fictitious or pseudo forces. I am not completely comfortable about this.  I can't help thinking that by using this terminology and this view of inertial frames we are actually missing or misunderstanding the whole picture.

Ultimately, just about everything spins, or is a part of something that spins, so the universe is in general a non-inertial frame of reference and yet we try to do most of our work in an inertial frames of reference because, lets face it, the calculations are easier and they are a good every day approximation. By doing this though I think that we are closing our minds to something far larger and potentially revealing. The fact that it is more complex is our failing to interpret and describe it properly, in reality it is no more complex.

Imaginary friends

There are some names that just do justice to the subject they describe. Worse still is a name that can actually detract from the subject. Take imaginary numbers for instance.  For me this has got to be one of the worst names ever.

For those unaccustomed to these little fellas, these numbers are the result of taking the square root of a negative number. For example, the square root of -4 is not -2. After all

(-2) x (-2) = 4

the square root of -4 is 2i so

(2i) x (2i) = 4i² = 4 x (-1) = -4, because i x i = i² = -1

so any number that is the square root of a negative number is called... imaginary. We say that they do not exist, so they are imaginary. A trick of mathematics, if you will. This, for me, is where we are going wrong.

There is nothing imaginary about these number they are just a different branch of mathematics and for physics they are invaluable. Without them it is impossible to describe photons mathematically. Electric and magnetic fields just don't work. Quantum mechanics would probably not exist at all.

Yet I find that when we talk about the "imaginary" component of a vector or field or whatever something in my brain discounts it almost. It is as if my brain is saying , yep, it allows us to describe something mathematically, but it does not exist in the real world. A bit like saying that atoms are not real but just mathematical abstractions, which is complete nonsense.

The universe is built on imaginary numbers, so they cannot be imaginary, I can see them at work every time I look at the sun or the moon or pretty much anything. You try describing anything and sooner or later the imaginary number will raise its head. Not only that but it also pops up in one of the most, if not the most amazing of equations.

Now, it has been noted that I do go in for a bit of mathematician bashing, but on this occasion I salute them, get a load of this

This is known as Euler's identity or Euler's equation. This equation has addition, multiplication and an exponential. It contains five fundamental mathematical constants:

• The number 0, the additive identity.
• The number 1, the multiplicative identity.
• The number π,  (π = 3.14159265...)
• The number e, the base of natural logarithms, which occurs widely in mathematical and scientific analysis (e = 2.718281828...). Both π and e are transcendental numbers.
• The number i, the imaginary unit.

Some consider it to be one of the most beautiful equations of all and I find myself agreeing with them. It says so much in such a small equation, a little like E=mc².

Also,

e^iπ = cos π + i sin π  which is just a specific solution of
e^iωt = cos ωt + i sin ωt
which is the starting point of describing how a photon travels through space.

So, imaginary numbers give us beautiful equations and help us to explain the universe... Can this be right? maybe I am imagining it after all.

Sometimes equations get in the way

I was having a drink the other night with a mathematician and we where discussing the many differences between physics people and maths people, and for me, this is probably one of the better examples. I go into a shop with my friend the mathematician, he tries to place his order.

See if you can figure out what this is (answer at the bottom)...

Mathematician says (this is nicked straight from Wiki)...

In geometry, a torus (pl. tori) is a surface of revolution generated by revolving a circle in three dimensional space about an axis coplanar with the circle. In most contexts it is assumed that the axis does not touch the circle - in this case the surface has a ring shape and is called a ring torus or simply torus if the ring shape is implicit.


A torus can be defined parametrically by:

where

u,v are in the interval [0, 2π),

R (or A) is the distance from the center of the tube to the center of the torus,

r (or a) is the radius of the tube.

R and r are also known as the "major radius" and "minor radius", respectively. The ratio of the two is known as the "aspect ratio".

He goes further...

An implicit equation in Cartesian coordinates for a torus radially symmetric about the z- axis is

or the solution of , where

Algebraically eliminating the square root gives a quartic equation,

The three different classes of standard tori correspond to the three possible relative sizes of r and R. When R > r, the surface will be the familiar ring torus.

At this point the physicist steps up and says

"Give me one of those..."

a personal favorite

strictly speaking we were describing on of these,

A torus, bit like a doughnut if you ask me

but you get the idea. Now my friend argues that his definition can be understood by everyone who understands the language of mathematics anywhere in the universe.

I argue that the language required may be so complex that it can blind people to what we are actually trying to get across.

At this time I think that sometimes, just sometimes we have to much of the mathematician in physics when what we really need is a physicist.  Nice doughnut by the way.

Lasers

Laser is an acronym of Light Amplification by Stimulated Emission of Radiation. These days you will find lasers for cutting, welding, barcode readers, in CD and DVD players, in guidance systems, lithography, holography, surgery,  scanners and even optical tweezers, plus about a thousand other uses and places.

There are lots of different types including gas lasers, chemical lasers, solid state lasers, fiber lasers, excimer lasers, photonic crystal lasers, semiconductor lasers, dye lasers, free electron laser and bio lasers.

In the modern world the laser can be found just about everywhere it seems. Due to mass production of diode lasers you can now get them for very little. I bought a laser guided spirit level the other day for under $10! Diode lasers out sell all other laser put together by about 5000 to 1!

It is due to their wide scale use of lasers that I thought it may be worth putting together a blog to this amazing piece of physics.

The original  idea for a laser was published in 1917 by Albert Einstein after he'd done some pondering on work by Max Planck. You have to give it to Albert Einstein, he had the knack of investigating and contributing to many of the great aspects of physics, you have to wonder if he was just really lucky, or a really bright guy, a genius perhaps? Anyway, back to lasers.

Light is made up of photons of all different frequencies. The different frequencies appear to our light detectors (more commonly known as eyes) as the different colours.

Electrons orbit round a positive nucleus in something we call atoms. An electron can move from a lower energy state into a higher energy state and visa versa. When it moves from the high energy state to the low energy state it gives out a photon. If you get lots of these photons you have something the eye can detect. In a light bulb, electricity is used to energize the electrons and when they drop into lower energy levels we get light. It comes out in all different frequencies and so it appears to our eyes as white light. This is known in the trade as the spontaneous emission of photons.

A laser is a special version of this process. In a laser the electrons become energized in much the same way, through electricity or some other source. But that is where the similarity ends. In the case of a laser, light is emitted by a process we call stimulated emission. In this case an electron in the higher orbit drops into the lower orbit because of the presence of a photon of exactly the same energy as the difference between the two energy levels.

A photon causes a stimulated emission resulting in 2 photons

When the electron drops a photon is produced that is identical to the first and they add like waves to give a more intense wave. This process continues in something similar to an avalanche and before you know it you have a really intense beam of light with a single frequency (this is known as monochromatic) and that is a laser.


While this process may seem relatively simple to understand now, it was a remarkable piece of deduction by Einstein and some equally clever practical physics from the people who actually turned the theory into working lasers.

3 level laser

The trick is how to get the electrons into the higher energy state. See the problem is that as fast as you push them up they will start to fall back down. Thermodynamics shows that this is the case and that you can never get more electrons in the E₂ level than in the E₁ level. Which means that you don't get a a laser.

The solution is really clever. Find a material that has 3 energy levels. Pump from level 1 into the level 3 using light or electricity. The electrons fall back into level 2 (not level 1) giving out heat. By doing this you can get more electrons in level 2 than level 1. When this happens you have something called population inversion, which is the required condition for a laser. You then introduce photons with the same energy as the gap between level 2 and level 1 and bingo, you cause stimulated emissions to occur.

That's all well and good, now all we have to do is find a material with this magical level structure and they do actually exist, a ruby is a good example. The first lasers were based on ruby. They were very inefficient, but they did work. Further investigation lead to the realization that there were a number of materials that could be used to create lasers, including semiconductors.

Semiconductors define 20th century electronics for me, which is odd in a way because they are actually very poor conductors, they have been used in just about every computerized electrical device in the world. Given that there are tens of billions of devices based on semiconductor electronics you soon see that they are literally everywhere.

The semiconductor lasers work on something called a p-n junction diode, which will be covered in a post of its own. Experiments on this material led to the discovery that it could be used as a light source, converting electrical energy into light energy. It was then only a smallish step to create a p-n diode laser. These are by far the most common lasers in the world. While these may be made of silicon and not ruby and while they cost less than $10 they are based on the same principle, pumping electrons into an energized state that the drop down into the lower energy state giving off light of a fixed frequency.

It is odd that these days people take lasers pretty much for granted, you can buy them on the internet.  We have lasers in just about every computer and every CD or DVD player. Yet they are based on some brilliant theoretical and practical physics. We really should not forget this because without these brilliant men we would not have all these fantastic toys.

Positronium - seriously

PET scanners love positronium

Positronium, you just couldn't make this stuff up if you tried. It reminds me of Unobtainium, which is pretty close.

Talking of which, was it just me or was the Unobtainium in Avatar actually a room temperature superconductor?

The difference here of course is that positronium, unlike Unobtainium or Handwavium, is actually real, sort off. I say sort off because its life time is so unimaginable short. If something exists you get the idea that you could take a look at it, give it a prod and so on, but not with positronium.

Positronium comes in a couple of variations. It is always an electron/positron pair, but, just like an atom, it can exist in different energy states. The energy state determines just how long positronium survives. The problem is that the positron (first postulated by Dirac) is the antiparticle of an electron and as soon as the electron and positron get close enough they annihilate each other completely.

This annihilation happens very quickly after the positronium has formed. The longest surviving state is the 2S state and lasts for about 1 micro second, that is 1 millionth of a second. A very short time. In 1 millionth of a second light can travel about 300 meters because the speed of light is so fast. The shortest surviving form of Positronium is known as para-positronium and lasts for about 125 picoseconds.

125 picoseconds is an extremely short period of time. A picosecond is a millionth of a millionth of a second. So using the speed of light again, in 125 picoseconds, light would travel 37.5 mm, which is about 1.5 inchs, about the length of your thumb. Not very far because 125 picoseconds is not very long at all.

Now, you may be thinking to yourself, fair enough, it has a cool name and all, but what use is something that only hangs around long enough for light to travel the length of my thumb? Well, you may be surprised to find that it does have some use in the real world. See, when the electron and the positron annihilate each other they give off high energy photons, known in the trade as gamma rays and have a clearly defined energy.

PET scan of a brain

By measuring the gamma rays that result and by using some my numbingly clever analysis you can actually build up a picture of the inside of a person. This process is known as Positron Emission Tomography  and the device for taking the measurements is often known as a PET Scanner.
PET scanners have a number of uses particularly in oncology for obtaining images of tumors as well as the detection of brain diseases. It is also used in cancer research.

In medicine it is possible to introduce positronium into a human being using something called a radionuclide (a radioactive material). The radionuclide is often a glucose based material such as flourine-18 floourodeoxyglucose (FDG). Once the FDG enters a cell it becomes trapped until it decays. (When it decays it gives out a positron which interacts with an electron to form positronium. The positron and electron then annihilate each other to produce gamma rays.) This means that tissues that have a high uptake of glucose, the brain, liver and most cancers can be clearly seen.


While positronium is of interest from a physics point of view it has also been used in some really clever practical applications.

It is amazing to think that we have been able to make use of something that lasts only long enough for light to travel the length of your thumb and from this we can actually determine brain diseases and cancers!

How cool is that?

Wave Particle Duality

A particle or a wave?

Wave particle duality is one of those things that I can't help thinking we haven't got quite right. I think that this may also be the reason why it confuses so many people. It is a subject that has no place in every day experience, there is nothing in every day life that can give you the idea that a particle could actually behave like a wave.

In fact there is not much in life to give you any real experience of particles. It actually took until 1905 for Einstein to provide a method to show that atoms actually existed and as it turned out were very very small indeed.

During most of the 17th, 18th and 19th centuries arguments about the nature of light went back and forth, was it particle like? was it wave like? It seemed to be both yet people tended to side with one idea or the other. Newton was firmly in the camp of the particle.

Eventually a guy called Taylor decided to try and settle it using a variation of Young wave experiment. In 1909 he placed two very small holes right next to each other and shone light through them. They created a wave interference pattern, just like the type of thing you get in water when two waves overlap. So, light is a wave, job done. Not so fast, that was only the first part of the experiment.

Next he got some exceptionally sensitive film and repeated the experiment. For bright light, interference patten as expected. But for really dim light the photos showed tiny pinpoints of light scattering out of the holes, making it seem like light was in fact particles. It gets stranger, when he exposed the film to the dim light for a long time he ended up with an interference pattern again! In other words light was behaving like particles and waves. So was everyone right?!

It gets even odder, Louis de Broglie then said well if light can behave like particles and waves, maybe particles such as electrons can behave like waves. Experiments were performed and lo and behold if Louis isn't right. Electrons can behave just as if they are waves.

So it seems, from experiment that light and particles can be both waves and particles.

What is the physical interpretation of this? Is de Broglie correct? Certainly seems that way.

Has anything changed to alter our opinions? We've had about 80 years or so to ponder this one, so is wave-particle duality still consider the correct interpretation of the observations?

In quantum mechanics we have the good old Schrödinger equation (covered in more detail in another post) which is based on the idea of something called a "wave function". As the name suggests this is based on the idea of waves and can explain things like interference and diffraction pattens. What is cool though is that it can also explain the particle behaviour of particles. So this definitely adds weight to the idea.

That said ... we still don't really know for sure.

It is true that Quantum mechanics has done fantastically well since its discovery and because of this most physicists accept the wave particle duality argument but there are some who are not convinced.

Louis De Broglie extended his original idea to show that there is no duality. Light is not a wave or a particle, but both simultaneously, similarly an electron is both a particle and a wave at the same time, not one or the other.

Some believe that duality can be replaced by wave only and that we are just misinterpreting particle behaviour. Take a look at superconductivity, this seems to be governed by a quantum mechanical wave, same goes for lasers, yet these are what we call macroscopic, in other words they are operating in dimensions far larger than those we normally associate with quantum mechanics.

There is no doubt from experiment that light can behave like a particle or a wave, same goes for an electron. What is in doubt is the physical interpretation of these observations. As yet no one has been able to come up with an experiment, or been able to interpret the results from existing experiments, to conclusively say which argument is correct.

May be the answer is that it is not possible to give an definitive interpretation, I hope not, I'd feel as though the universe had cheated! May be we are still missing some clue that will give us a new insight or explanation of the results. May be, may be, may be.... don't you just love physics.